Well control has been a major obstacle for introducing dual gradient systems for deep water drilling, involving both new and more complex procedures and equipment. Here test results using a new dual gradient drilling (DGD) system to control simulated well control events are presented. After successfully drilling a Statoil well with Enhanced Drilling's dual gradient solution (EC-Drill) at the Troll (Kjøsnes et al. 2014) field on the Norwegian continental shelf, the well was plugged and made ready for 48 hours of controlled testing. Several tests were run, each designed to determine the functionality of the system; to detect and handle liquid loss, gas and liquid influx, gas migration in the riser, and circulation of gas through the subsea pump module. The detection tests were carried out with a reduced riser level and an open annular, to quantify the capability of the system to detect volume imbalances while drilling. Three circulation tests with increasing amount of gas injected through the drillstring were performed. After the influx was detected, the annular was closed, and the flow was routed from the well through a bypass line to the subsea pump module. A topside choke in the mud return line was actively used to apply backpressure with the objective to control bottom-hole pressure, while circulating the gas from the well. In the last test gas was allowed to migrate into the marine drilling riser with a reduced riser level and open annular.
The paper will present the planning and preparations as well as the results.